The investigation into a former Clackamas County student accused in Florida of threatening mass murder began with a tip from a student, Clackamas County Sheriff Craig Roberts said today.

Calin Chi Wong, 20, was arrested March 27 in Homstead, Fla., after posting an Internet message threatening to undertake a Virginia Tech-style massacre. Florida officers found a weapons cache at his home that included four AK-47s and 5,000 rounds of ammunition.

The investigation began March 25, when Clackamas County sheriff's deputies received a call about the disturbing posting on a Web site for gun enthusiasts. Police did not disclose the source of the tip other than to say it was a concerned student.

A Clackamas County sheriff's deputy who called Wong at his home in Florida found him "calm and cooperative," Roberts said, adding that Wong was worried about losing his federal firearms license.

Wong has no criminal record in Clackamas County, according to Detective Jim Strovink, a sheriff's spokesman. He lived in Oregon for several years before moving to Florida, according to Strovink.